I've looked at my old original WordPerfect files and indeed I have "obtabilem" with a "b" (instead of "optabilem" with a "p"). So it's not a misprint: it's a mistake. (Google gives c 1,250 pages for "p"; it gives 8 for "b" - one of which is this page.) Thanks for pointing this out, Cesare. There's a guy doing an annotated version of AS,TB - I'll point him to this entry.